Combat vehicle gunnery sight



a? 33am. (in- 793O8a635 5R LE CH HOQI Jan. 19, 1943. R. c. WALKER2,308,635

COMBAT VEHICLE GUNNERY SIGHT V Filed Nov. 15, 1940 2 Sheets-Sheet lINVENTOR. ROBERT awn/cam n Aurm search mm \JU ULUHIL 1 HHJAL. Hm) IHUWILH I01 Jan. 19, 1943. R. c. WALKER COMBAT VEHICLE GUNNERY SIGHTFiled Nov. 15, 1940 2 Sheets-Sheet 2 ROBERT GYM/619540 WlL/lE/P w? 0 V AT TOR/V5) Patented Jan' 19, 1943 UNITED STATES PATENT @H 'EQE 6 Claims.

This invention relates to an improved gun sight for a combat vehicle, asfor example, a combat aeroplane or mechanized land vehicle.

Such vehicles have, of course, transverse and longitudinal axes normallylying in a horizontal plane with one or more guns mounted at variousparts of the vehicle with the axis of the gun barrel commonly parallelto the longitudinal axis and perpendicular to the transverse axis of thevehicle. When such vehicles are on an even keel, that is, when the axistransverse to the axis of the gun barrel lies in its normal horizontalplane accurate fire can be obtained. When, however, the transverse axisof the Vehicle, which axis is in turn transverse to the axis of the gunbarrel, rotates in a plane which intersects the normal horizontal plane,or in other words when the longitudinal axis (or axis of translation) ofthe vehicle parallel to the axis of the gun barrel constitutes an aXisabout which the vehicle rotates as a whole, serious inaccuracies of fireoccur. Such rotation is commonly met with in aerial combat, as forexample When firing occurs from a plane undergoing a steep bank. Suchrotation may also occur in the case of an armored land vehicle, as forexample when firing occurs from a tank which is inclined about itslongitudinal axis.

The reason for such inaccuracy will more fully appear by reference toFigs. 11 and 12 of the accompanying drawings. Fig. 11 showsdiagrammatically a conventional form of rear sight and front sight on anarmored vehicle resting on an even keel, that is, with the longitudinaland transverse axes of the vehicle lying in their normal horizontalplane. The rear circular sight comprises a reticule or line I-2 and thefront sight a post 6. Line "I represents the axis of the what may betermed the plane of sight, and in Fig. 11 this plane of sight isvertical and coincides with the plane containing the trajectory of thebullet.

Fig. 12 shows diagrammatically the result of rotation of the gun barrelwith its attached rear sight and front sight 6 about an axis parallel tothe axis of the gun barrel or bore through an angle subtended betweenthe lines l-2 and 9-2. The line l2 and the plane passing through thisline and front sight 6 (which also rotates) do not remain vertical andundergo a rotation and the rotated plane contains the lines ll' and 22'.The line 8 shows the trajectory of the projectile, the line I is anextension of the axis of the bore of the gun and 3' indicates the objectaimed at. Since the reticule represented by the line l2 in Figs. 11 and12 is in fixed relation to the gun, rotation of the latter about an axisparallel to the bore causes displacement of the point I, as shown inFig. 12. This point corresponds to the position of the rear sight formaximum range, and the line of sight which connects the point I and thecenter of the front sight 6 when projected ends at the point I. Thetriangles l-3Ei and l' 3'-6 are similar triangles and it will thereforebe seen that as a result of the rotation, the error (for maximum range)is magnified in proportion to the distance of the object from the frontsight, which will be readily observed by comparing the respectivelengths of the lines l3' and l-3 in Fig. 12.

In short, as a result of the rotation, the gunner sights at the targetin one direction while the trajectory of the projectile takes adifferent direction.

It has been discovered that if the plane of sight is maintained in avertical position parallel to or coplanar with the plane of thetrajectory, the error can be obviated and it will be noted that theerror is caused by the fact that the plane of sight passing through thefixed vertical reticule or line I2 and the front sight 6 does not remainvertical and coincidental with or parallel to the vertical plane of thetrajectory when the plane rotates, but undergoes an angular movement inrelation to the vertical plane of the trajectory in the mannerdescribed.

It is an object of the present invention to maintain the plane of sightin a vertical position so that this plane is either parallel to thevertical plane containing the trajectory of the bullet and inpredetermined fixed relation thereto or coincident with the plane ofsaid trajectory. Stated otherwise, it is an object of the invention tomaintain, when the vehicle undergoes the rotation described, a relationbetween the plane containing the trajectory of the bullet and the planeof sight, which is substantially or in practical effect the samerelation which exists when the Vehicle is on an even keel.

It is a further object to provide means whereby the plane of sight isalways in a vertical position and in coplanar relation to the plane ofthe trajectory irrespective of rotation of the axis of the gun barrelabout an axis parallel thereto, that is to say, irrespective of therotation of the transverse axis of the vehicle in a plane intersectingthe horizontal plane in which said axis normally lies.

It is a further object to provide a combination of gun sight and rangefinder, the said range finder affording means for determiningautomatically or by simple mental calculation the range of the object.

It is a further object of the invention to provide a telescopic gunsight to magnify the image of the object in addition to overcoming theerror due to rotation above described.

Further objects and advantages will hereinafter appear.

In accordance with the invention, the gun sight for a vehicle of theclass described comprises a closed, light-transmitting conduit having acircular axis, this conduit being adapted to be rigidly mounted inrelation to the gun barrel, the circular axis of the conduit lying in aplane perpendicular to the axis of the gun barrel, together with meanswithin said conduit providing in effect a point establishing a line ofsight connecting said point with the object aimed at, said line of sightlying in a vertical plane of sight containing the center of saidcircular axis, said plane being coincident with the vertical planecontaining the trajectory of the projectile fired from the gun when thetransverse axis of the vehicle occupies its normal position in ahorizontal plane, and means within said conduit to maintain said planeof sight in a substantially vertical position coincident with Orparallel to the plane of the trajectory, irrespective of rotation of thevehicle about its longitudinal axis.

The principles of the invention will be set forth in the claims andillustrative embodiments of these principles will be set forth in thefollowing description. taken in conjunction with the drawings, in which:

Fig. 1 show an elevation of a preferred form of rear gun sight of thepresent invention;

Fig. 2 shows a side elevation;

Fig. 3 is a section on the line 3-3 of Fig. 1;

Fig. 4 is a top View of Fig. 1 partly in section;

Figs. 5 and 7 are side and front elevational views of a preferred formof front sight;

Fig. 6 is a section on the line 6-6 of Fig. 7;

Figs. 8 and 9 are top views of a tandem assembly of front sights.

Fig. 10 is a section on the line Ill-l0 of Fig. 13;

Figs. 11 and 12 are diagrammatic views to assist in explaining theadvantages and principles of the invention;

Fig. 13 is a sectional elevational view of a telescopic sight; and

Fig. 14 illustrates a construction in which the circular axis of theconduit or hollow ring of the invention is concentric with the axis ofthe gun bore.

' Referring to Fig. l, the rear sight there shown comprises a hollowring l2 made of transparent glass or plastic material filled withmercury except for a space of any predetermined and convenientdimensions constituting the bubble 13 which i floated in the mercury.The ring I2 has a circular axis and a circular cross section. The hollowring may be filled with mercury with the aid of a tubulature, not shown,through which mercury is introduced into the ring, which tubulature isthen sealed off leaving a protuberance M, as shown in Fig. 3. The ringmay be mounted in a base l5, said base comprising a lower receivingportion l6 and a cooperating upper portion or saddle l1, screws l8 beingprovided to clamp the saddle to the lower portion l6 of the base I 5. Anannular guard l 9 is preferably provided and secured in place togetherwith the hollow ring by means of the base I5. The ring and base may bemounted on any part of the vehicle with the circular axis of the ringlying in a plane perpendicular to the axis of the bore of the gun orguns. The facts that the center of the ring is located in spacedrelation to the axis or axes of the gun bore or bores introduces anerror which varies as the distance from the center of the ring to theaxis of the gun. Combat vehicles are frequently provided with aplurality of guns. For example, an aeroplane may have a gun positionedon or closely adjacent to the cockpit and one or more other guns atvarious other portions of the plane, as for example in the wings. Thesight comprising the ring l2 and base i 5 may be mounted directly uponone of the guns with the center of the ring only a few inches from theaxis of the bore. If the vehicle has another gun or guns locatedsomewhere remote from the rear sight the distance from the center of thering l2 to the axis of the bore of that gun or those guns will, ofcourse, be greater, but whatever error is occasioned by the distancebetween the center of the ring and the bore of the gun will always be aconstant regardless of the range, and negligible in amount. In otherwords, the plane of sight containing the center of the bubble l3 and thecenter of the ring will always be vertical and either coincidental withor parallel to the plane of the trajectory of the bullet as contrastedwith the divergence or angular relation of the plane of sight and theplane of the trajectory of the bullet which characterizes a rear sightin a fixed position, this divergence and consequent magnification oferror proportional to the range having been already alluded to above inconnection with Figs. 11 and 12.

Consequently the rear sight of the present invention may be located onany part of the vehicle and it is not necessary that it be mounted onany particular gun or on any gun. The plane containing the circular axisof the ring I2 should, however, be perpendicular to the axis of the boreof the gun, and the axis of translation of the vehicle.

Mercury has been specifically mentioned as the preferred liquid fillingfor the hollow ring I 2, and while mercury is distinctly preferred onaccount of its combination of high specific gravity and high surfacetension with low viscosity or mobility, other liquids may be employed.

The column or filling of mercury remains in substantially the sameposition irrespective of the rotation of the hollow ring I2 caused byangular rotation of the vehicle about its longitudinal axis (or axis oftranslation), and the walls of the ring move in relation to the columnof mercury so that there is a relative movement of these walls inrelation to the mercury. The coefiicient of friction between the mercuryand the transparent walls, when these are of glass, is so low that thebubble l3 always remains substantially in a vertical plane passingthrough the center of this bubble and the center of the ring, and thisplane which also contains the center of the front sight is the plane ofsight which 33. GEUMLI HIUAL \No l numnw IO.

has already been mentioned. Consequently, the mercury column constitutesand embodies means within the conduit or hollow ring to maintain saidplane of sight in a substantially vertical position irrespective ofrotation of the vehicle about its longitudinal axis (or axis oftranslation) parallel to the plane of sight, or otherwise stated,rotation of the transverse axis of the vehicle in a plane intersectingthe horizontal plane in which said axis normally lies.

Instead of mercury other liquids possessing the necessary qualities oflow viscosity and low coeflicient of friction in relation to the wallsof the ring, preferably in combination with surface tension and highspecific gravity, may be employed, as for example various kinds oforganic and inorganic liquids.

The bubble I3 constitutes and embodies a species of body ofpredetermined dimensions floated by the liquid. Preferably this body isfluid, that is, a liquid immiscible with the mercury or its equivalent,or a gas. In the specific embodiment shown in the drawings the said bodyI3 is a gaseous bubble and it may be advantageously one of the raregases, as for example neon, although nitrogen or other inert gas or airwill be satisfactory. If desired the gas may be enclosed within atransparent globule or envelope.

A gaseous body or bubble I3 is more advantageous than a liquid or solidbecause the extremely low specific gravity of the gas in relation to thehigh specific gravity of the mercury makes it possible for the center ofsaid bubble always to remain in the same vertical plane passing throughthe center of this bubble and the center of the hollow ring, that is,there is substantially no lag or drag, or tendency of the bubble tofollow the walls of the ring in their annular movement caused byrotation of the vehicle about its longitudinal axis. Moreover, it ispossible to impart to the gaseous bubble l3 a high degree of luminosityand contrast in relation to its adjacent environment or background. Thismay be done by discharging through the gaseous bubble a high frequencyinduced current produced by the coil 22 provided with high frequencycurrent from any suitable source, not shown. The presence of the mercurywill cause the gaseous bubble to emit light having the characteristicsof the mercury spectrum.

The invention also provides, in combination with the sight, a device forestimating the range of the target. In the specific form shown in Fig. 1this device includes the post 24 extending from the base I andterminating in a hollow ring 25, the center of which ring is the centerof the ring I2. This post carries a frame 26 having a series of points,as shown, arranged in a circle in concentric and spaced relation to thecircular axis of the ring. These points are spaced apart equidistant andthe distance between any two points is of course predetermined andknown. Consequently, if an object having known dimensions comes into therange of vision, its relation to these points affords a basis forestimating the range of the object. In aerial combat, for example, thedimensions of an enemy plane are generally known from its type and thedevice described therefore enables the operator to estimate or mentallycalculate the range.

Preferred forms of a front sight employed in the present invention areshown in Figs. 5 to 9 inclusive. This preferred form includes a socket30 carrying an incandescent bulb 3|, a hollow post 32 and a base 33. Aninsulated wire 34 Search contacts with the shank 35 of the incandescentbulb which, of course, constitutes one terminal thereof. The otherterminal or base contacts with the socket 30 through the boss 36 and thesocket 30 is grounded to the body of the vehicle through the post 32 andbase 33. To provide against movement of the bulb 3| the terminal of thewire 34 is provided with a wire spiral 36 enclosed within a tubularcovering of resilient and insulating material such as rubber whichengages a recess 31 in the socket 30.

Current for the illumination of the incandescent bulb 3| as well as forenergizing the high frequency coil 22 may be provided by any suitablesource which it is not necessary to specifically show in the drawingsand describe.

As shown in Figs. 8 and 9, it may be desirable to have a tandem assemblyof front sights so that in the event that one is shot away the remainingsight will still be available.

The mode of operation will now be described in the light of the priordescription and. with further reference to diagrammatic Figs. 11 and 12:

Assuming that the vehicle is on even keel with its longitudinal axis(axis of translation) lying in its normal horizontal plane the operatorestimates the range of the enemy object, which may for example be anenemy plane, by means of the range finding device 26 and then sightsthrough any point in the vertical plane passing through the middle ofthe bubble I3 and. the center of the ring I2 (which is also the centerof the ring 25) and the center of the front sight, said point beingintermediate between the bubble I3 and the center of the ring I2 forintermediate range, at the center of the bubble I3 for maximum range,and through the center of the ring 25 for point-blank range. This planeof sight is coincident with the plane of the trajectory of the bulletwhen the vehicle is on even keel and it is therefore necessary only tocorrect for the fall of the bullet or its trajectory. When the vehiclerotates about its axis of translation or longitudinal axis, if the bodyor point I3 were in fixed relation to the ring the plane of sight wouldof course undergo a corresponding rotation, as illustrated in Fig. 12 bythe line I-2. The trajectory of the bullet, shown by the line 8 in Fig.12, still remains in a vertical plane but the plane of sight containingthe lines I-2 and I'-2', as shown in Fig. 12, is not in a vertical planebut on the contrary in a plane which intersects the vertical plane ofthe trajectory at an angle. Consequently the plane of trajectoryprogressively diverges from the plane of sight depending on the degreeof rotation of the vehicle and the range of the target, thus introducinga serious and indeterminate error.

In the present invention, however, the center of the body or bubble I3,shown in Fig. 1, always remains in the same vertical plane containingthe center of said bubble I3, the center of the ring 25, and the centerof the front sight, irrespective of rotation of the ring I2 caused bycorresponding rotation of the vehicle about its axis of translationparallel to the bore of the gun and transverse to the plane containingthe circular axis of said ring I2. As the ring I2 rotates, the plane oftrajectory which as already stated always remains vertical,progressively moves away from the plane of sight to an extent dependentupon the degree of inclination of the vehicle from the horizontal planebut these two planes, the plane of sight and the plane of the trajectoryalways remain in parallel vertical and coplanar relationship so thatthere is no magnification of the error due to the distance between theseparallel planes which is determinate and can be allowed for. When thesight is mounted on the barrel of the gun the maximum possible distancebetween these two parallel vertical planes is very small, as for examplea matter of a few inches. If the sight is mounted on a given portion ofthe vehicle and the gun being fired is mounted at a remote portion ofthe vehicle the distance between these two planes, that is, the plane ofsight and the plane of trajectory may be a matter of a few feet or a fewyards, but again, this distance is constant and determinate, and in thecase of aerial combat gunnery, where a number of guns are mounted atvarious points and their fire controlled by the present invention, theslight dispersion of fire cause by the plurality of guns is a distinctadvan tage.

This is again illustrated by reference to Fig. 12 in which 3 representsthe bubble |3 shown in Fig. 1 and shown in Figs. 11 and 12, represents afixed point on the circumference of the ring |2 which, as shown in Figs.11 and 12, represents a ring sight mounted directly upon a gun in closeproximity to the barrel, the bore of which is represented by line inFigs. 11 and 12. In these Figs. 11 and 12 the solid crossed lines of thering l2 represent the conventional crossed wire reticule. As the ring l2rotates, the bubble l3 of Fig. 1 (represented as 3 in Fig. 12) remainsin the same vertical plane containing the dotted lines 34 and 3 of Fig.12. This vertical plane is in coplanar parallel relation to the verticalplane of the trajectory of the bullet containing the lines 29 and 1.

Consequently the error caused by the distance between the vertical planeof the trajectory of the bullet and the vertical plane of sight isalways constant. When the sight is mounted directly on the gun thedistance between these planes is not only constant but is negligible,and where the sight is mounted at a point on the vehicle remote from thegun being fired the error, while greater, is still constant and can bereadily allowed for if desired, and in many cases is advantageous, asabove explained.

If desired, it is possible to eliminate even the constant anddeterminate error measured by the distance between the vertical plane ofsight and the vertical coplanar plane of the trajectory. This can bedone by constructing the hollow circular conduit or ring so that itscircular axis is concentric with the bore of the gun on which it ismounted, and in such case the said hollow conduit may wholly surroundthe barrel of the gun or only partially. However, it is believed to beconvenient, usually, not to attempt such concentric relation but tomount the sight on any desired portion of the vehicle and make properallowance for the constant, determinate error previously described wheresuch error is anything more than negligible.

Fig. 14 shows a structure in which the hollow conduit 50 carrying thebubble 5| floated in a suitable body of liquid, e. g. mercury, isconcentrically arranged in relation to the bore of the gun barrel 55. Ahanger having a strap 57 and a clamping portion 58 is suspended from thegun barrel 55 by means of a circular strap 54. The clamping portion 58carries the hollow ring so that the latter is concentric with the boreof the gun. There is preferably used in combination with this rear sightcomprising the hollow conduit 50, a front sight comprising an annularring 53 carrying radial arms 56 joined to a second annular ring (notspecifically shown) mounted on the gun barrel, the said annular ring 53being also concentric with the bore. In using the device shown in Fig.14 the center of the bubble 5| and the intersection of an arm 56 withthe ring 53 may be used as the points respectively determining the lineof sight for maximum range, and for intermediate ranges the rear sightwill be any point between the center Of the bubble 5| and the saidintersection of an arm 56 with the ring 53. The image of the front sightcomprising the ring 53 and arms 56 appears to the observer to lieconcentrically within the hollow conduit 50, and the arms 56 provide notonly front sights but also radial arms, any point along which (or theprojection of which) may be selected as the rear sight. If desired, asecond annular ring 52 having a circular axis lying in the same plane asthe circular axis of the hollow conduit 50 may be provided and supportedon the gun barrel in the same manner as the front sight.

Figs. 10 and 13 show a form of the invention in which the sightdescribed is mounted within the barrel or tube 40 of a telescope havingan objective lens 4| and an eye piece 42, the particular telescopeelements shown in Figs. 10 and 13 being substantially those of aGalilean telescope represented diagrammatically. The hollow ring I3 isconstructed similarly to that shown in Fig. 1 except that the base l5cooperates with an adjustment device 43 to permit the sight to beadjusted in proper focused and spaced relation to the objective and eyepiece so that both the hollow ring and target may be viewedcoincidentally. A post 44 extends from the base I5 and terminates in anannular ring 45 in substantially the same manner as the post 24 and ring25 shown in Fig. 1.

I claim:

1. A rear gun sight for a combat vehicle, said vehicle having atransverse axis normally lying in a horizontal plane, a gun mounted onsaid vehicle and a front sight on said gun, said rear gun sightcomprising a closed light-transmitting conduit having a circular axis;said conduit being adapted to be rigidly mounted in relation to the gunbarrel, the circular axis of said conduit lying in a plane transverse tothe axis of the gun barrel; said conduit containing therewithin meansproviding, in effect, a point establishing with the front sight a lineof sight connecting said point with the object aimed at, said line ofsight lying in a vertical plane of sight containing the center of saidcircular axis and the front sight, said plane being coincident with thevertical plane containing the trajectory of the projectile fired fromsaid gun when the transverse axis of the vehicle occupies its normalposition in a horizontal plane; and liquid means within said conduitfioatingly supporting said first named means to maintain said plane ofsight in a vertical position substantially coincident with the plane ofthe trajectory irrespective of inclination of the transverse axis of thevehicle from its normal horizontal position.

2. A rear gun sight for a combat vehicle, said vehicle having atransverse axis normally lying in a horizontal plane, a gun mounted onsaid vehicle and a front sight on said gun, said rear gun sightcomprising a closed light-transmitting conduit having a circular axis;said conduit being 33. GEOMETRiCAL lNSl liUMtNlS.

adapted to be rigidly mounted in relation to the gun barrel, thecircular axis of said conduit lying in a plane transverse to the axis ofthe gun barrel; said conduit containing therewithin means providing, ineffect, a point establishing with the front sight a line of sightconnecting said point with the object aimed at, said line of sight lyingin a vertical plane of sight containing the center of said circular axisand the front sight, said plane being coincident with the vertical planecontaining the trajectory of the projectile fired from said gun when thetransverse axis of the vehicle occupies its normal position in ahorizontal plane; and means within said conduit to maintain said planeof sight in a vertical position substantially coincident with the planeof the trajectory irrespective of inclination of the transverse axis ofthe vehicle from its normal horizontal position, said means comprising acolumn of mobile liquid and a body of predetermined dimensions floatedby said liquid.

3. A rear gun sight for a combat vehicle, said vehicle having atransverse axis normally lying in a horizontal plane, a gun mounted onsaid vehicle and a front sight on said gun, said rear gun sightcomprising a closed light-transmitting conduit having a circular axis;said conduit being adapted to be rigidly mounted in relation to the gunbarrel, the circular axis of said conduit lying in a plane transverse tothe axis of the gun barrel; said conduit containing a floating bodyproviding, in effect, a point establishing with said front sight a lineof sight connecting said point with the object aimed at, said line ofsight lying in a vertical plane of sight containing the center of saidcircular axis and the front sight, said plane being coincident with thever tical plane containing the trajectory of the projectile fired fromsaid gun when the transverse axis of the vehicle occupies its normalposition in a horizontal plane; and liquid means within said conduit tomaintain said plane of sight in a vertical position substantallycoincident with the plane of the trajectory irrespective of inclinationof the transverse axis of the vehicle from its normal horizontalposition, said means comprising a column of mobile liquid on which saidfirst named means is floated; and means to render said floated bodyclearly visible and in sharp contrast to the column of liquid.

4. A rear gun sight for a combat vehicle, said vehicle having atransverse axis normally lying in a horizontal plane, a gun mounted onsaid vehicle and a front sight on said gun, said rear sight comprising aclosed light-transmitting conduit having a circular axis; said conduitbeing adapted to be rigidly mounted in relation to the gun barrel, thecircular axis of said conduit lying in a plane transverse to the axis ofthe gun barrel; said front sight comprising a luminous substantiallyspherical body; said conduit containing a gaseous bubble floated thereinproviding, in effect, a point establishing with said front sight a lineof sight connecting said point with the front sight and the object aimedat, said line of sight lying in a vertical plane of sight containing thecenter of said circular axis and the front sight, said plane beingcoincident with the vertical plane containing the trajectory of theprojectile fired from said gun when the transverse axis of the vehicleoccupies its normal position in a horizontal plane; and liquid meanswithin said conduit to maintain said plane of sight in a verticalposition substantially coincident with the plane of the trajectoryirrespective of inclination of the transverse axis of the vehicle fromits normal horizontal position, said means comprising a column ofmercury on which said bubble is floated; and means to render luminoussaid floated gaseous bubble.

5. A combination of gun sight and range finder for a combat vehiclehaving a transverse axis normally lying in a horizontal plane, a gunmounted on said vehicle and a front sight on said gun, the axis of thegun barrel being substantially transverse to the said axis of thevehicle, said combination comprising a hollow ring having transparentwalls constituting a conduit path having a circular axis and a circularcross section; a base on which said ring is mounted, said base beingadapted to mount the ring in rigid and spaced relation to the gunbarrel, with the circular axis of the ring lying in a plane transverseto the axis of the gun barrel; a post extending from the base and havinga terminus at the center of the ring; said conduit containing a mobileliquid and a gaseous bubble floated in said liquid whereby a planepassing through the center of said bubble, the center of the terminus ofsaid post and the front sight constitutes a plane of sight which remainsvertical and substantially coincident with the plane of the trajectoryirrespective of the inclination of the transverse axis of the vehiclefrom its normal horizontal position; said post carrying a frame having aseries of points arranged in a circle in concentric and spaced relationto the circular axis of the ring, the distance between any two of saidpoints affording means to determine the range of an object having knowndimensions.

6. A telescopic gun sight for a combat vehicle having a transverse axisnormally lying in a horizontal plane and a gun mounted on said vehicle,comprising a hollow ring having transparent walls constituting a conduithaving a circular axis and a circular cross section; a post extendingfrom the circumference of said ring and having a terminus at the centerof the ring; said conduit containing a mobile liquid and a gaseousbubble floated in said liquid whereby a plane passing through the centerof said bubble and the center of the terminus of said post constitutes aplane of sight which remains vertical and substantially coincident withthe plane of the trajectory irrespective of the inclination of thetransverse axis of the vehicle from its normal, horizontal position; atelescope having an objective lens and an eye-lenfiggsaidrihg be- -ingmounted within said telescope" between the objective lens and eye lenswith the circular axis of the conduit lying in a plane transverse to theaxis of the telescope; and means to translate the ring along the axis ofthe telescope to adjust the position of the ring in relation to saidlenses.

ROBERT CRAIGHEAD WALKER.

